1. Field of the Invention
One of the more common forms of oil recovery used is sucker rod pumping, wherein a sucker rod string is employed in a well bore and carries at the bottom end thereof a positive displacement pump. The sucker rod string and pump are reciprocated up and down inside the well tubing. The result is that the product in the well tubing is forced upwardly through the tubing to the earth's surface.
The sucker rod string is reciprocated through the use of a pumping unit located at the earth's surface. This requires the sucker rod string to be reciprocated through an opening in the well head that caps the well tubing at the earth's surface. A seal commonly referred to as "packing" is universally employed in this area to prevent well fluids and gases from escaping from around the sucker rod string and out of the well.
Typically, the sucker rod seal employs packing elements that are mechanically forced against a polished rod. The packing elements press against the polished rod and achieve a tight seal therewith to prevent, to the maximum extent possible, leakage from the interior of the well head around the polished rod and then to the exterior of the well head. The packing elements are typically forced against the polished rod in what is known as a stuffing box. Because the polished rod moves repeatedly up and down through these packing elements over a long period of time, the elements are subject to mechanical wear so that the stuffing box requires frequent monitoring to adjust or replace worn packing elements to ensure leakage prevention. To extend the life of the stuffing box seals, the packing elements must be lubricated. A difficulty that arises during start up of the well is that portions of the stuffing box may not yet be lubricated, which results in wear on the packing elements due to friction caused by the reciprocating polished rod.
It is commonly known that the service life of the polished rod is extended if a polished rod liner is employed. One hazard of the use of a polished rod liner is that in the event a polished rod breaks or slips out of the polished rod clamp, the liner will fall and the polished rod liner head will impact the top of the stuffing box resulting in possible damage to the stuffing box. When stuffing boxes are damaged or wear out they subsequently allow liquids and gases to escape. Today's stricter environmental requirements demand that steps be taken to prevent the escape of hydrocarbon gases and liquids from the well bore.
Another problem which affects the service life of packing in a stuffing box is the influx of particulate matter, such as sand or dirt into the stuffing box. On the down stroke, this abrasive material often sticks to the wet surface of the polished rod or liner and is carried into the stuffing box which hastens wear on the packing.
2. Background
There exist several patents which attempt to solve the problem of hydrocarbons escaping from around the polished rod. Patents such as U.S. Pat. No. 5,217,069 for a "Sucker Rod Wiper", and U.S. Pat. No. 4,982,787 for a "Pipe Wiper System", are all intended to be used for the purpose of wiping a sucker rod string during a well pumping operation. None of these devices are intended for mounting on top of a stuffing box. Additionally, none of the devices described in these patents are designed for shock absorption or polished rod lubricating.
Another patent that disclosed an apparatus designed to prevent hydrocarbons from escaping from around the polished rod is U.S. Pat. No. 4,345,766 entitled: "Apparatus for Sealing an Oil Well Pump Polishing Rod." This device is actually an improved stuffing box as is U.S. Pat. No. 5,170,853, for a "Pipe Wiper Assembly for a Well Drilling Unit" which is designed to replace the stuffing box on a rotary drilling rig.
U.S. Pat. No. 3,032,112 entitled "Oil Saver Shock Absorber" is a device which is placed below the stuffing box. This device is designed to prevent the impact against the bottom of the stuffing box of tools removed from the well bore. These tools are commonly raised until the upper-most portion of the tool strikes the lower extremity of the line-stripper apparatus which is attached to the casing-head. The device is not intended to protect the stuffing box from the impact of the polished rod liner head in the event that the polished rod breaks. Additionally, this device does not possess a means for lubricating the polished rod. Further, it is not designed to protect the stuffing box from foreign material or prevent product from escaping into the environment.
Finally, there exist patented devices to protect the polished rod so that it does not pick up abrasive materials which may be subsequently drawn into the stuffing box. U.S. Pat. No. 3,353,606 to Dyer teaches a polished rod protector. However, this device is not configured to provide protection from damage from the impact from the polished rod liner head in the event of polished rod breakage above the stuffing box. Furthermore, the device does not possess a means for lubricating the polished rod.